Antimatter mine

An antimatter mine was a relatively small antimatter weapon used by Starfleet, the size of a small probe that contained a large quantity of antimatter. On board sensors detected close-range starships and the mine moved towards them. On impact, the containment fields within the mine collapsed, dispersing antimatter onto the ship's hull, causing a large number of instant annihilations, resulting in an explosion.

The object pictured is actually a US Naval Sonobuoy shipping container. These heavy plastic containers are generally disposed of once the expendable contents are unpacked for use. The TV and film industry has used these cheap and plentiful containers for years in many science fiction productions. They often are used as special plot devices, interior set components, and most often as generic cargo containers.